In order to modify the lift characteristics of an airfoil for low speed operation, leading edge airfoil devices are used on the aircraft wing leading edge to pivot or slide outwardly from the leading edge of the airfoil to a deployed position. Typically, these leading edge slats are moved downward and forward from the wing leading edge. Movement of the slat is caused by a linear actuator between the wing and the slat, or by a rotary actuator which moves a track or arm which is attached to the slat. During extension and retraction of the slat, it is desirable that the location of the trailing edge of the slat remain on or near the upper surface of the wing to prevent air flow turbulence on the wing upper surface and thereby reduce aerodynamic drag.
In certain moderate angle of attack configurations when the slat is fully extended, the trailing edge of the slat is spaced apart from the upper surface of the wing to form a small aerodynamic slot. This slot permits the introduction of high energy air from beneath the wing over the upper surface of the wing. This high energy airflow assists in keeping the airflow attached the upper surface of the wing to maintain the lift capability of the wing at lower aircraft speeds. To maintain wing lift for very low speed, high angle of attack configurations, the slat is rotated to a steeper angle to further increase the distance between the slat trailing edge and the wing upper surface thereby increasing the size of the aforementioned slot and the amount of high energy air available to prevent the wing from stalling.
In conventional leading edge slat apparatus, additional programming tracks are required to rotate the slat to the optimum angle for various medium and high lift configurations. These programming track assemblies are typically quite large and heavy thereby increasing the overall gross weight of the aircraft. In addition, the rate at which the slat is moved into the medium and high lift configurations is limited by the actuator speed.